1. Field of the Invention
The present invention relates to a lens array. In particular, it relates to a lens array of the type which is used in an optical device such as a contact-type image sensor for focusing the images on a document onto linearly arranged light receiving elements. The present invention also relates to a method of making such a lens array and a lens.
2. Description of the Related Art
A conventional lens array of the above-mentioned type is provided with a plurality of lenses which are produced separately from each other. These lenses are arranged in an array and held together by a holder which is prepared separately from the lenses. The lenses may be convex lenses made of glass, while the holder may be made of a synthetic resin. In place of the convex lenses, a plurality of self-focusing lenses (rod lenses) may be used for producing the image of an object in a non-inverting and non-magnifying manner.
The conventional lens array is disadvantageous in the following points.
Specifically, the production procedure of the conventional lens array tends to be unduly complicated since the respective lenses and the holder are produced separately from each other. The smallness of each lens (the diameter may often be smaller than 1 mm) and the multiplicity of the lenses aggravate the situation. As readily understood, it is very difficult to accurately position a great number of small lenses within the holder.
Another drawback of the conventional lens array is that light tends to be unduly scattered at the lens surface of each lens due to unevenness of the lens surface. With the use of such a lens array, reproduction of a clear image cannot be expected.
The present invention has been proposed under the abovedescribed circumstances, and its object is to produce, efficiently and at low costs, lens arrays or lenses exhibiting an excellent optical performance.
According to a first aspect of the present invention, there is provided a lens array comprising: a plurality of lenses each of which is provided with a lens surface; a holder portion for fixing the lenses; and a transparent layer for covering at least the lens surface of each lens.
With such an arrangement, the lens surface of each lens is smoothed out by the transparent layer, which is advantageous to improving the optical performance of the lens. The transparent layer may be made of an acrylic material.
Preferably, the holder portion and the lenses may be made of a same transparent resin material and formed as a one-piece element. A lens array having such features is readily produced by a molding technique. Thus, in comparison with the conventional lens array, the production efficiency is improved and the production costs are advantageously reduced.
Preferably, a light shielding layer may further be formed on at least part of the holder portion. The light shielding layer serves to prevent unwanted light from entering or leaving the lens array.
Preferably, the holder portion may be provided with a plurality of grooves, wherein each of the lenses is located between two grooves. Further, each of the grooves may be provided with inner wall surfaces covered by the light shielding layer. With such an arrangement, the cross talk of light is prevented, which improves the optical performance of the lens array.
Preferably, the light shielding layer may be rendered dark-colored (in particular, black) for facilitating the absorption of unwanted light.
Preferably, the transparent layer may overlap the light shielding layer. In this manner, the light shielding layer is protected by the transparent layer from mechanical damage, while also being secured to the holder portion or the lenses under the transparent layer.
Preferably, the lens array of the present invention may further comprise engaging means for associating with an additional lens array. With such an arrangement, a lens array assembly is readily constituted by combining more than one lens array.
Preferably, each of the lenses may be provided with first and second lens surfaces which are unequal in diameter to each other.
According to a second aspect of the present invention, there is provided a method of making a lens array. The method comprises the steps of: molding a transparent resin material into a resin element provided with a plurality of lenses; and forming a transparent layer for covering at least a lens surface of each lens.
Preferably, the method may further comprise a step of dividing the resin element into a plurality of lens arrays.
Preferably, the transparent layer may be formed by spraying a transparent acrylic material onto the lens surface of each lens. In this manner, the acrylic material can be uniformly applied over a wide area. In general, an acrylic paint material has advantageously high transparency. Also, an acrylic paint is easy to handle and less expensive than other materials, which is advantageous to reducing the production costs.
Preferably, the viscosity of the acrylic material may be in a range of 10 mP-100 mP at 20xc2x0 C.
Preferably, the method of the present invention may further comprise a step of forming a light shielding layer on the resin element before the forming of the transparent layer.
Preferably, the transparent layer may overlap the light shielding layer. With such an arrangement, the transparent layer, which is arranged on the light shielding layer, prevents the light shielding layer from peeling off.
Preferably, the light shielding layer may be formed by ejecting dark-colored ink onto the resin element. The ejecting of the ink may be performed by an inkjet printer.
According to a third aspect of the present invention, there is provided a lens comprising: a transparent body provided with a lens surface; and a transparent layer covering the lens surface.
The lens surface may be curved. For instance, the lens surface may be convex or concave.
Other features and advantages of the present invention will become apparent from the detailed description given below with reference to the accompanying drawings.